Systems and Methods of Fine Grained Interception of Network Communications on a Virtual Private Network

ABSTRACT

A method for intercepting communication of a client to a destination on a virtual private network includes an agent executing on the client that intercepts a network communication of the client. The agent provides a virtual private network connection from a first network to a second network. The decision to intercept is based on a network destination description or an identification of an application authorized to be accessed via the virtual private network. In one case, the agent determines that a destination specified by the intercepted communication corresponds to a network identifier and a port of a network destination description of an application on the second network authorized for access via the virtual private network. In response to this determination, the agent transmits the intercepted communication.

FIELD OF THE INVENTION

The present invention generally relates to secure data communicationnetworks and, in particular, to systems and methods for increasing thesecurity of data communication networks by intercepting SSL/VPN datacommunications on a more granular basis.

BACKGROUND OF THE INVENTION

Virtual private networks provide users of a client computer with secureaccess to remote resources when public networks. Many virtual privatenetworks use network appliances to provide secure connections toclients. For example, a user may access resources includingapplications, web sites, and files by connecting to a network appliancewhich manages a number of virtual private network connections. In manycases, an agent program associated with the client identifies networkcommunications intended for the virtual private network based on theaddress used to send the communication.

However, this technique suffers from a number of drawbacks. Because alltraffic corresponding to an address range is sent to the virtual privatenetwork, whether appropriately sent to the network or not, robustauthorization policies must be created to filter appropriate virtualprivate network traffic from traffic that should not be sent on thevirtual private network. Such policies are difficult to create anddifficult to maintain. Also, blanket routing of all data communicationto a virtual private network, whether appropriate or not, can increasesecurity risks, since a malicious user may use data traffic having thecorrect address range to cause harm to the data center the virtualprivate network is meant to protect.

It would, therefore, be desirable to provide systems and methods toroute data in a virtual private network environment on a more granularbasis than subnet identification.

BRIEF SUMMARY OF THE INVENTION

In one aspect, the present invention relates to a method forintercepting communication of a client to a destination on a virtualprivate network. The decision to intercept is based on a networkdestination description of an application authorized to be accessed viathe virtual private network. An agent executing on the client interceptsa network communication of the client. The agent provides a virtualprivate network connection from a first network to a second network. Theagent determines that a destination specified by the interceptedcommunication corresponds to a network identifier and a port of anetwork destination description of an application on the second networkauthorized for access via the virtual private network. In response tothis determination, the agent transmits the intercepted communication.

In some embodiments, the agent determines that the network communicationdoes not correspond to the network destination description of theapplication and transmits the intercepted network communication via thefirst network. In other embodiments, the agent determines that thenetwork communication does not correspond to the network destinationdescription of the application and drops the intercepted networkcommunication. In still other embodiments, the agent determines that thenetwork identifier and the port of the client correspond to a sourceinternet protocol address and a source port of the network destinationdescription of the application. In still other embodiments, the agentdetermines a type of protocol for which the network communication isformatted corresponds to a protocol specified by the network destinationdescription of the application. In yet other embodiments, the agentdetermines not to intercept a second network communication of the clientdestined to a second application not authorized for access to the secondnetwork via the virtual private network connection. In some of theseembodiments, the agent intercepts network communication transparently toone of the application or a user of the client.

In another aspect, the present invention relates to a method forprovides a level of access, by an appliance, access to a resource by anapplication on a client via a virtual private network connection. Adecision to allow or deny a level of access is based on identificationof the application. The appliance intercepts a request from anapplication on a client on a first network to access via a virtualprivate network connection a resource on a second network. The applianceidentifies the application and associates with the intercepted requestan authorization policy based on the identity of the application. Theappliance determines, using the authorization policy and the identity ofthe application, to either allow or deny access by the application tothe resource.

In some embodiments, the agent transmits a name of the application tothe appliance. In further of these embodiments, name of the applicationis used as the identifier of the application. In other embodiments, theagent establishes the virtual private network connection to the secondnetwork via the appliance. In still other embodiments, an authorizationpolicy specifies a name of the application and an authorization toeither access or deny a level of access. In some of these embodiments,the appliance associates the authorization policy of the applicationwith a user of the client. In others of these embodiments, the applianceidentifies the authorization policy of the application based on a userof the client.

In yet another aspect, the present invention relates to a method forintercepting, by an agent of a client, communications from the client tobe transmitted via a virtual private network connection. Theinterception is based on identification of an application from which thecommunication originates. The agent receives information identifying afirst application. The agent determines a network communicationtransmitted by the client originates from the first application andintercepts that communication. The agent transmits the interceptedcommunication via the virtual private network connection.

The details of various embodiments of the invention are set forth in theaccompanying drawings and the description below.

BRIEF DESCRIPTION OF THE FIGURES

The foregoing and other objects, aspects, features, and advantages ofthe invention will become more apparent and better understood byreferring to the following description taken in conjunction with theaccompanying drawings, in which:

FIG. 1A is a block diagram of an embodiment of a network environment fora client to access a server via an appliance;

FIG. 1B is a block diagram of an embodiment of an environment fordelivering a computing environment from a server to a client via anappliance;

FIGS. 1C and 1D are block diagrams of embodiments of a computing device;

FIG. 2A is a block diagram of an embodiment of an appliance forprocessing communications between a client and a server;

FIG. 2B is a block diagram of another embodiment of an appliance foroptimizing, accelerating, load-balancing and routing communicationsbetween a client and a server;

FIG. 3 is a block diagram of an embodiment of a client for communicatingwith a server via the appliance;

FIG. 4 is a block diagram of an embodiment of a client-side fine-grainedinterception mechanism;

FIG. 5 is a flow diagram depicting steps of an embodiment of a methodfor practicing client-side fine-grained interception techniques; and

FIG. 6 is a flow diagram depicting steps of an embodiment of a methodfor practicing a technique for providing levels of access to anapplication by an appliance based on identification of the application.

The features and advantages of the present invention will become moreapparent from the detailed description set forth below when taken inconjunction with the drawings, in which like reference charactersidentify corresponding elements throughout. In the drawings, likereference numbers generally indicate identical, functionally similar,and/or structurally similar elements.

DETAILED DESCRIPTION OF THE INVENTION A. Network and ComputingEnvironment

Prior to discussing the specifics of embodiments of the systems andmethods of an appliance and/or client, it may be helpful to discuss thenetwork and computing environments in which such embodiments may bedeployed. Referring now to FIG. 1A, an embodiment of a networkenvironment is depicted. In brief overview, the network environmentcomprises one or more clients 102 a-102 n (also generally referred to aslocal machine(s) 102, or client(s) 102) in communication with one ormore servers 106 a-106 n (also generally referred to as server(s) 106,or remote machine(s) 106) via one or more networks 104, 104′ (generallyreferred to as network 104). In some embodiments, a client 102communicates with a server 106 via an appliance 200.

Although FIG. 1A shows a network 104 and a network 104′ between theclients 102 and the servers 106, the clients 102 and the servers 106 maybe on the same network 104. The networks 104 and 104′ can be the sametype of network or different types of networks. The network 104 and/orthe network 104′ can be a local-area network (LAN), such as a companyIntranet, a metropolitan area network (MAN), or a wide area network(WAN), such as the Internet or the World Wide Web. In one embodiment,network 104′ may be a private network and network 104 may be a publicnetwork. In some embodiments, network 104 may be a private network andnetwork 104′ a public network. In another embodiment, networks 104 and104′ may both be private networks. In some embodiments, clients 102 maybe located at a branch office of a corporate enterprise communicatingvia a WAN connection over the network 104 to the servers 106 located ata corporate data center.

The network 104 and/or 104′ be any type and/or form of network and mayinclude any of the following: a point to point network, a broadcastnetwork, a wide area network, a local area network, a telecommunicationsnetwork, a data communication network, a computer network, an ATM(Asynchronous Transfer Mode) network, a SONET (Synchronous OpticalNetwork) network, a SDH (Synchronous Digital Hierarchy) network, awireless network and a wireline network. In some embodiments, thenetwork 104 may comprise a wireless link, such as an infrared channel orsatellite band. The topology of the network 104 and/or 104′ may be abus, star, or ring network topology. The network 104 and/or 104′ andnetwork topology may be of any such network or network topology as knownto those ordinarily skilled in the art capable of supporting theoperations described herein.

As shown in FIG. 1A, the appliance 200, which also may be referred to asan interface unit 200 or gateway 200, is shown between the networks 104and 104′. In some embodiments, the appliance 200 may be located onnetwork 104. For example, a branch office of a corporate enterprise maydeploy an appliance 200 at the branch office. In other embodiments, theappliance 200 may be located on network 104′. For example, an appliance200 may be located at a corporate data center. In yet anotherembodiment, a plurality of appliances 200 may be deployed on network104. In some embodiments, a plurality of appliances 200 may be deployedon network 104′. In one embodiment, a first appliance 200 communicateswith a second appliance 200′. In other embodiments, the appliance 200could be a part of any client 102 or server 106 on the same or differentnetwork 104,104′ as the client 102. One or more appliances 200 may belocated at any point in the network or network communications pathbetween a client 102 and a server 106.

In one embodiment, the system may include multiple, logically-groupedservers 106. In these embodiments, the logical group of servers may bereferred to as a server farm 38. In some of these embodiments, theserves 106 may be geographically dispersed. In some cases, a farm 38 maybe administered as a single entity. In other embodiments, the serverfarm 38 comprises a plurality of server farms 38. In one embodiment, theserver farm executes one or more applications on behalf of one or moreclients 102.

The servers 106 within each farm 38 can be heterogeneous. One or more ofthe servers 106 can operate according to one type of operating systemplatform (e.g., WINDOWS NT, manufactured by Microsoft Corp. of Redmond,Wash.), while one or more of the other servers 106 can operate onaccording to another type of operating system platform (e.g., Unix orLinux). The servers 106 of each farm 38 do not need to be physicallyproximate to another server 106 in the same farm 38. Thus, the group ofservers 106 logically grouped as a farm 38 may be interconnected using awide-area network (WAN) connection or medium-area network (MAN)connection. For example, a farm 38 may include servers 106 physicallylocated in different continents or different regions of a continent,country, state, city, campus, or room. Data transmission speeds betweenservers 106 in the farm 38 can be increased if the servers 106 areconnected using a local-area network (LAN) connection or some form ofdirect connection.

Servers 106 may be referred to as a file server, application server, webserver, proxy server, or gateway server. In some embodiments, a server106 may have the capacity to function as either an application server oras a master application server. In one embodiment, a server 106 mayinclude an Active Directory. The clients 102 may also be referred to asclient nodes or endpoints. In some embodiments, a client 102 has thecapacity to function as both a client node seeking access toapplications on a server and as an application server providing accessto hosted applications for other clients 102 a-102 n.

In some embodiments, a client 102 communicates with a server 106. In oneembodiment, the client 102 communicates directly with one of the servers106 in a farm 38. In another embodiment, the client 102 executes aprogram neighborhood application to communicate with a server 106 in afarm 38. In still another embodiment, the server 106 provides thefunctionality of a master node. In some embodiments, the client 102communicates with the server 106 in the farm 38 through a network 104.Over the network 104, the client 102 can, for example, request executionof various applications hosted by the servers 106 a- 106 n in the farm38 and receive output of the results of the application execution fordisplay. In some embodiments, only the master node provides thefunctionality required to identify and provide address informationassociated with a server 106′ hosting a requested application.

In one embodiment, the server 106 provides functionality of a webserver. In another embodiment, the server 106 a receives requests fromthe client 102, forwards the requests to a second server 106 b andresponds to the request by the client 102 with a response to the requestfrom the server 106 b. In still another embodiment, the server 106acquires an enumeration of applications available to the client 102 andaddress information associated with a server 106 hosting an applicationidentified by the enumeration of applications. In yet anotherembodiment, the server 106 presents the response to the request to theclient 102 using a web interface. In one embodiment, the client 102communicates directly with the server 106 to access the identifiedapplication. In another embodiment, the client 102 receives applicationoutput data, such as display data, generated by an execution of theidentified application on the server 106.

Referring now to FIG. 1B, a network environment for delivering and/oroperating a computing environment on a client 102 is depicted. In someembodiments, a server 106 includes an application delivery system 190for delivering a computing environment or an application and/or datafile to one or more clients 102. In brief overview, a client 10 is incommunication with a server 106 via network 104, 104′ and appliance 200.For example, the client 102 may reside in a remote office of a company,e.g., a branch office, and the server 106 may reside at a corporate datacenter. The client 102 comprises a client agent 120, and a computingenvironment 15. The computing environment 15 may execute or operate anapplication that accesses, processes or uses a data file. The computingenvironment 15, application and/or data file may be delivered via theappliance 200 and/or the server 106.

In some embodiments, the appliance 200 accelerates delivery of acomputing environment 15, or any portion thereof, to a client 102. Inone embodiment, the appliance 200 accelerates the delivery of thecomputing environment 15 by the application delivery system 190. Forexample, the embodiments described herein may be used to acceleratedelivery of a streaming application and data file processable by theapplication from a central corporate data center to a remote userlocation, such as a branch office of the company. In another embodiment,the appliance 200 accelerates transport layer traffic between a client102 and a server 106. The appliance 200 may provide accelerationtechniques for accelerating any transport layer payload from a server106 to a client 102, such as: 1) transport layer connection pooling, 2)transport layer connection multiplexing, 3) transport control protocolbuffering, 4) compression and 5) caching. In some embodiments, theappliance 200 provides load balancing of servers 106 in responding torequests from clients 102. In other embodiments, the appliance 200 actsas a proxy or access server to provide access to the one or more servers106. In another embodiment, the appliance 200 provides a secure virtualprivate network connection from a first network 104 of the client 102 tothe second network 104′ of the server 106, such as an SSL VPNconnection. It yet other embodiments, the appliance 200 providesapplication firewall security, control and management of the connectionand communications between a client 102 and a server 106.

In some embodiments, the application delivery management system 190provides application delivery techniques to deliver a computingenvironment to a desktop of a user, remote or otherwise, based on aplurality of execution methods and based on any authentication andauthorization policies applied via a policy engine 195. With thesetechniques, a remote user may obtain a computing environment and accessto server stored applications and data files from any network connecteddevice 100. In one embodiment, the application delivery system 190 mayreside or execute on a server 106. In another embodiment, theapplication delivery system 190 may reside or execute on a plurality ofservers 106 a-106n. In some embodiments, the application delivery system190 may execute in a server farm 38. In one embodiment, the server 106executing the application delivery system 190 may also store or providethe application and data file. In another embodiment, a first set of oneor more servers 106 may execute the application delivery system 190, anda different server 106 n may store or provide the application and datafile. In some embodiments, each of the application delivery system 190,the application, and data file may reside or be located on differentservers. In yet another embodiment, any portion of the applicationdelivery system 190 may reside, execute or be stored on or distributedto the appliance 200, or a plurality of appliances.

The client 102 may include a computing environment 15 for executing anapplication that uses or processes a data file. The client 102 vianetworks 104, 104′ and appliance 200 may request an application and datafile from the server 106. In one embodiment, the appliance 200 mayforward a request from the client 102 to the server 106. For example,the client 102 may not have the application and data file stored oraccessible locally. In response to the request, the application deliverysystem 190 and/or server 106 may deliver the application and data fileto the client 102. For example, in one embodiment, the server 106 maytransmit the application as an application stream to operate incomputing environment 15 on client 102.

In some embodiments, the application delivery system 190 comprises anyportion of the Citrix Access Suite™ by Citrix Systems, Inc., such as theMetaFrame or Citrix Presentation Server™ and/or any of the Microsoft®Windows Terminal Services manufactured by the Microsoft Corporation. Inone embodiment, the application delivery system 190 may deliver one ormore applications to clients 102 or users via a remote-display protocolor otherwise via remote-based or server-based computing. In anotherembodiment, the application delivery system 190 may deliver one or moreapplications to clients or users via steaming of the application.

In one embodiment, the application delivery system 190 includes a policyengine 195 for controlling and managing the access to, selection ofapplication execution methods and the delivery of applications. In someembodiments, the policy engine 195 determines the one or moreapplications a user or client 102 may access. In another embodiment, thepolicy engine 195 determines how the application should be delivered tothe user or client 102, e.g., the method of execution. In someembodiments, the application delivery system 190 provides a plurality ofdelivery techniques from which to select a method of applicationexecution, such as a server-based computing, streaming or delivering theapplication locally to the client 120 for local execution.

In one embodiment, a client 102 requests execution of an applicationprogram and the application delivery system 190 comprising a server 106selects a method of executing the application program. In someembodiments, the server 106 receives credentials from the client 102. Inanother embodiment, the server 106 receives a request for an enumerationof available applications from the client 102. In one embodiment, inresponse to the request or receipt of credentials, the applicationdelivery system 190 enumerates a plurality of application programsavailable to the client 102. The application delivery system 190receives a request to execute an enumerated application. The applicationdelivery system 190 selects one of a predetermined number of methods forexecuting the enumerated application, for example, responsive to apolicy of a policy engine. The application delivery system 190 mayselect a method of execution of the application enabling the client 102to receive application-output data generated by execution of theapplication program on a server 106. The application delivery system 190may select a method of execution of the application enabling the localmachine 10 to execute the application program locally after retrieving aplurality of application files comprising the application. In yetanother embodiment, the application delivery system 190 may select amethod of execution of the application to stream the application via thenetwork 104 to the client 102.

A client 102 may execute, operate or otherwise provide an application,which can be any type and/or form of software, program, or executableinstructions such as any type and/or form of web browser, web-basedclient, client-server application, a thin-client computing client, anActiveX control, or a Java applet, or any other type and/or form ofexecutable instructions capable of executing on client 102. In someembodiments, the application may be a server-based or a remote-basedapplication executed on behalf of the client 102 on a server 106. In oneembodiments the server 106 may display output to the client 102 usingany thin-client or remote-display protocol, such as the IndependentComputing Architecture (ICA) protocol manufactured by Citrix Systems,Inc. of Ft. Lauderdale, Fla. or the Remote Desktop Protocol (RDP)manufactured by the Microsoft Corporation of Redmond, Wash. Theapplication can use any type of protocol and it can be, for example, anHTTP client, an FTP client, an Oscar client, or a Telnet client. Inother embodiments, the application comprises any type of softwarerelated to VoIP communications, such as a soft IP telephone. In furtherembodiments, the application comprises any application related toreal-time data communications, such as applications for streaming videoand/or audio.

In some embodiments, the server 106 or a server farm 38 may be runningone or more applications, such as an application providing a thin-clientcomputing or remote display presentation application. In one embodiment,the server 106 or server farm 38 executes as an application, any portionof the Citrix Access Suite™ by Citrix Systems, Inc., such as theMetaFrame or Citrix Presentation Server™, and/or any of the Microsoft™Windows Terminal Services manufactured by the Microsoft Corporation. Inone embodiment, the application is an ICA client, developed by CitrixSystems, Inc. of Fort Lauderdale, Fla. In other embodiments, theapplication includes a Remote Desktop (RDP) client, developed byMicrosoft Corporation of Redmond, Wash. Also, the server 106 may run anapplication, which for example, may be an application server providingemail services such as Microsoft Exchange manufactured by the MicrosoftCorporation of Redmond, Wash., a web or Internet server, or a desktopsharing server, or a collaboration server. In some embodiments, any ofthe applications may comprise any type of hosted service or products,such as GoToMeeting™ provided by Citrix Online Division, Inc. of SantaBarbara, Calif., WebEX™ provided by WebEx, Inc. of Santa Clara, Calif.,or Microsoft Office Live Meeting provided by Microsoft Corporation ofRedmond, Wash.

The client 102, server 106, and appliance 200 may be deployed as and/orexecuted on any type and form of computing device, such as a computer,network device or appliance capable of communicating on any type andform of network and performing the operations described herein. FIGS. 1Cand 1D depict block diagrams of a computing device 100 useful forpracticing an embodiment of the client 102, server 106 or appliance 200.As shown in FIGS. 1C and 1D, each computing device 100 includes acentral processing unit 101, and a main memory unit 122. As shown inFIG. 1C, a computing device 100 may include a visual display device 124,a keyboard 126 and/or a pointing device 127, such as a mouse. Eachcomputing device 100 may also include additional optional elements, suchas one or more input/output devices 130 a-130 b (generally referred tousing reference numeral 130), and a cache memory 140 in communicationwith the central processing unit 101.

The central processing unit 101 is any logic circuitry that responds toand processes instructions fetched from the main memory unit 122. Inmany embodiments, the central processing unit is provided by amicroprocessor unit, such as: those manufactured by Intel Corporation ofMountain View, Calif.; those manufactured by Motorola Corporation ofSchaumburg, Ill.; those manufactured by Transmeta Corporation of SantaClara, Calif.; the RS/6000 processor, those manufactured byInternational Business Machines of White Plains, N.Y.; or thosemanufactured by Advanced Micro Devices of Sunnyvale, Calif. Thecomputing device 100 may be based on any of these processors, or anyother processor capable of operating as described herein.

Main memory unit 122 may be one or more memory chips capable of storingdata and allowing any storage location to be directly accessed by themicroprocessor 101, such as Static random access memory (SRAM), BurstSRAM or SynchBurst SRAM (BSRAM), Dynamic random access memory (DRAM),Fast Page Mode DRAM (FPM DRAM), Enhanced DRAM (EDRAM), Extended DataOutput RAM (EDO RAM), Extended Data Output DRAM (EDO DRAM), BurstExtended Data Output DRAM (BEDO DRAM), Enhanced DRAM (EDRAM),synchronous DRAM (SDRAM), JEDEC SRAM, PC100 SDRAM, Double Data RateSDRAM (DDR SDRAM), Enhanced SDRAM (ESDRAM), SyncLink DRAM (SLDRAM),Direct Rambus DRAM (DRDRAM), or Ferroelectric RAM (FRAM). The mainmemory 122 may be based on any of the above described memory chips, orany other available memory chips capable of operating as describedherein. In the embodiment shown in FIG. 1C, the processor 101communicates with main memory 122 via a system bus 150 (described inmore detail below). FIG. 1C depicts an embodiment of a computing device100 in which the processor communicates directly with main memory 122via a memory port 103. For example, in FIG. 1D the main memory 122 maybe DRDRAM.

FIG. 1D depicts an embodiment in which the main processor 101communicates directly with cache memory 140 via a secondary bus,sometimes referred to as a backside bus. In other embodiments, the mainprocessor 101 communicates with cache memory 140 using the system bus150. Cache memory 140 typically has a faster response time than mainmemory 122 and is typically provided by SRAM, BSRAM, or EDRAM. In theembodiment shown in FIG. 1C, the processor 101 communicates with variousI/O devices 130 via a local system bus 150. Various busses may be usedto connect the central processing unit 101 to any of the I/O devices130, including a VESA VL bus, an ISA bus, an EISA bus, a MicroChannelArchitecture (MCA) bus, a PCI bus, a PCI-X bus, a PCI-Express bus, or aNuBus. For embodiments in which the I/O device is a video display 124,the processor 101 may use an Advanced Graphics Port (AGP) to communicatewith the display 124. FIG. 1D depicts an embodiment of a computer 100 inwhich the main processor 101 communicates directly with I/O device 130via HyperTransport, Rapid I/O, or InfiniBand. FIG. 1D also depicts anembodiment in which local busses and direct communication are mixed: theprocessor 101 communicates with I/O device 130 using a localinterconnect bus while communicating with I/O device 130 directly.

The computing device 100 may support any suitable installation device116, such as a floppy disk drive for receiving floppy disks such as3.5-inch, 5.25-inch disks or ZIP disks, a CD-ROM drive, a CD-R/RW drive,a DVD-ROM drive, tape drives of various formats, USB device, hard-driveor any other device suitable for installing software and programs suchas any client agent 120, or portion thereof. The computing device 100may further comprise a storage device 128, such as one or more hard diskdrives or redundant arrays of independent disks, for storing anoperating system and other related software, and for storing applicationsoftware programs such as any program related to the client agent 120.Optionally, any of the installation devices 116 could also be used asthe storage device 128. Additionally, the operating system and thesoftware can be run from a bootable medium, for example, a bootable CD,such as KNOPPIX®, a bootable CD for GNU/Linux that is available as aGNU/Linux distribution from knoppix.net.

Furthermore, the computing device 100 may include a network interface118 to interface to a Local Area Network (LAN), Wide Area Network (WAN)or the Internet through a variety of connections including, but notlimited to, standard telephone lines, LAN or WAN links (e.g., 802.11,T1, T3, 56 kb, X.25), broadband connections (e.g., ISDN, Frame Relay,ATM), wireless connections, or some combination of any or all of theabove. The network interface 118 may comprise a built-in networkadapter, network interface card, PCMCIA network card, card bus networkadapter, wireless network adapter, USB network adapter, modem or anyother device suitable for interfacing the computing device 100 to anytype of network capable of communication and performing the operationsdescribed herein. A wide variety of I/O devices 130 a-130n may bepresent in the computing device 100. Input devices include keyboards,mice, trackpads, trackballs, microphones, and drawing tablets. Outputdevices include video displays, speakers, inkjet printers, laserprinters, and dye-sublimation printers. The I/O devices 130 may becontrolled by an I/O controller 123 as shown in FIG. 1C. The I/Ocontroller may control one or more I/O devices such as a keyboard 126and a pointing device 127, e.g., a mouse or optical pen. Furthermore, anI/O device may also provide storage 128 and/or an installation medium116 for the computing device 100. In still other embodiments, thecomputing device 100 may provide USB connections to receive handheld USBstorage devices such as the USB Flash Drive line of devices manufacturedby Twintech Industry, Inc. of Los Alamitos, Calif.

In some embodiments, the computing device 100 may comprise or beconnected to multiple display devices 124a- 124n, which each may be ofthe same or different type and/or form. As such, any of the I/O devices130 a-130 n and/or the I/O controller 123 may comprise any type and/orform of suitable hardware, software, or combination of hardware andsoftware to support, enable or provide for the connection and use ofmultiple display devices 124 a-124 n by the computing device 100. Forexample, the computing device 100 may include any type and/or form ofvideo adapter, video card, driver, and/or library to interface,communicate, connect or otherwise use the display devices 124 a-124 n.In one embodiment, a video adapter may comprise multiple connectors tointerface to multiple display devices 124 a-124 n. In other embodiments,the computing device 100 may include multiple video adapters, with eachvideo adapter connected to one or more of the display devices 124 a-124n. In some embodiments, any portion of the operating system of thecomputing device 100 may be configured for using multiple displays 124a-124 n. In other embodiments, one or more of the display devices 124a-124 n may be provided by one or more other computing devices, such ascomputing devices 100 a and 100 b connected to the computing device 100,for example, via a network. These embodiments may include any type ofsoftware designed and constructed to use another computer's displaydevice as a second display device 124 a for the computing device 100.One ordinarily skilled in the art will recognize and appreciate thevarious ways and embodiments that a computing device 100 may beconfigured to have multiple display devices 124 a-124 n.

In further embodiments, an I/O device 130 may be a bridge 170 betweenthe system bus 150 and an external communication bus, such as a USB bus,an Apple Desktop Bus, an RS-232 serial connection, a SCSI bus, aFireWire bus, a FireWire 800 bus, an Ethernet bus, an AppleTalk bus, aGigabit Ethernet bus, an Asynchronous Transfer Mode bus, a HIPPI bus, aSuper HIPPI bus, a SerialPlus bus, a SCI/LAMP bus, a FibreChannel bus,or a Serial Attached small computer system interface bus.

A computing device 100 of the sort depicted in FIGS. 1C and 1D typicallyoperate under the control of operating systems, which control schedulingof tasks and access to system resources. The computing device 100 can berunning any operating system such as any of the versions of theMicrosoft® Windows operating systems, the different releases of the Unixand Linux operating systems, any version of the Mac OS® for Macintoshcomputers, any embedded operating system, any real-time operatingsystem, any open source operating system, any proprietary operatingsystem, any operating systems for mobile computing devices, or any otheroperating system capable of running on the computing device andperforming the operations described herein. Typical operating systemsinclude: WINDOWS 3.x, WINDOWS 95, WINDOWS 98, WINDOWS 2000, WINDOWS NT3.51, WINDOWS NT 4.0, WINDOWS CE, and WINDOWS XP, all of which aremanufactured by Microsoft Corporation of Redmond, Wash.; MacOS,manufactured by Apple Computer of Cupertino, Calif.; OS/2, manufacturedby International Business Machines of Armonk, N.Y.; and Linux, afreely-available operating system distributed by Caldera Corp. of SaltLake City, Utah, or any type and/or form of a Unix operating system,among others.

In other embodiments, the computing device 100 may have differentprocessors, operating systems, and input devices consistent with thedevice. For example, in one embodiment the computer 100 is a Treo 180,270, 1060, 600 or 650 smart phone manufactured by Palm, Inc. In thisembodiment, the Treo smart phone is operated under the control of thePalmOS operating system and includes a stylus input device as well as afive-way way navigator device. Moreover, the computing device 100 can beany workstation, desktop computer, laptop or notebook computer, server,handheld computer, mobile telephone, any other computer, or other formof computing or telecommunications device that is capable ofcommunication and that has sufficient processor power and memorycapacity to perform the operations described herein.

B. Appliance Architecture

FIG. 2A illustrates an example embodiment of the appliance 200. Thearchitecture of the appliance 200 in FIG. 2A is provided by way ofillustration only and is not intended to be limiting. As shown in FIG.2, appliance 200 comprises a hardware layer 206 and a software layerdivided into a user space 202 and a kernel space 204.

Hardware layer 206 provides the hardware elements upon which programsand services within kernel space 204 and user space 202 are executed.Hardware layer 206 also provides the structures and elements which allowprograms and services within kernel space 204 and user space 202 tocommunicate data both internally and externally with respect toappliance 200. As shown in FIG. 2, the hardware layer 206 includes aprocessing unit 262 for executing software programs and services, amemory 264 for storing software and data, network ports 266 fortransmitting and receiving data over a network, and an encryptionprocessor 260 for performing functions related to Secure Sockets Layerprocessing of data transmitted and received over the network. In someembodiments, the central processing unit 262 may perform the functionsof the encryption processor 260 in a single processor. Additionally, thehardware layer 206 may comprise multiple processors for each of theprocessing unit 262 and the encryption processor 260. The processor 262may include any of the processors 101 described above in connection withFIGS. 1C and 1D. In some embodiments, the central processing unit 262may perform the functions of the encryption processor 260 in a singleprocessor. Additionally, the hardware layer 206 may comprise multipleprocessors for each of the processing unit 262 and the encryptionprocessor 260. For example, in one embodiment, the appliance 200comprises a first processor 262 and a second processor 262′. In otherembodiments, the processor 262 or 262′ comprises a multi-core processor.

Although the hardware layer 206 of appliance 200 is generallyillustrated with an encryption processor 260, processor 260 may be aprocessor for performing functions related to any encryption protocol,such as the Secure Socket Layer (SSL) or Transport Layer Security (TLS)protocol. In some embodiments, the processor 260 may be a generalpurpose processor (GPP), and in further embodiments, may be haveexecutable instructions for performing processing of any securityrelated protocol.

Although the hardware layer 206 of appliance 200 is illustrated withcertain elements in FIG. 2, the hardware portions or components ofappliance 200 may comprise any type and form of elements, hardware orsoftware, of a computing device, such as the computing device 100illustrated and discussed herein in conjunction with FIGS. 1C and 1D. Insome embodiments, the appliance 200 may comprise a server, gateway,router, switch, bridge or other type of computing or network device, andhave any hardware and/or software elements associated therewith.

The operating system of appliance 200 allocates, manages, or otherwisesegregates the available system memory into kernel space 204 and userspace 204. In example software architecture 200, the operating systemmay be any type and/or form of Unix operating system although theinvention is not so limited. As such, the appliance 200 can be runningany operating system such as any of the versions of the Microsoft®Windows operating systems, the different releases of the Unix and Linuxoperating systems, any version of the Mac OS® for Macintosh computers,any embedded operating system, any network operating system, anyreal-time operating system, any open source operating system, anyproprietary operating system, any operating systems for mobile computingdevices or network devices, or any other operating system capable ofrunning on the appliance 200 and performing the operations describedherein.

The kernel space 204 is reserved for running the kernel 230, includingany device drivers, kernel extensions or other kernel related software.As known to those skilled in the art, the kernel 230 is the core of theoperating system, and provides access, control, and management ofresources and hardware-related elements of the application 104. Inaccordance with an embodiment of the appliance 200, the kernel space 204also includes a number of network services or processes working inconjunction with a cache manager 232. sometimes also referred to as theintegrated cache, the benefits of which are described in detail furtherherein. Additionally, the embodiment of the kernel 230 will depend onthe embodiment of the operating system installed, configured, orotherwise used by the device 200.

In one embodiment, the device 200 comprises one network stack 267, suchas a TCP/IP based stack, for communicating with the client 102 and/orthe server 106. In one embodiment, the network stack 267 is used tocommunicate with a first network, such as network 108, and a secondnetwork 1 10. In some embodiments, the device 200 terminates a firsttransport layer connection, such as a TCP connection of a client 102,and establishes a second transport layer connection to a server 106 foruse by the client 102, e.g., the second transport layer connection isterminated at the appliance 200 and the server 106. The first and secondtransport layer connections may be established via a single networkstack 267. In other embodiments, the device 200 may comprise multiplenetwork stacks, for example 267 and 267′, and the first transport layerconnection may be established or terminated at one network stack 267,and the second transport layer connection on the second network stack267′. For example, one network stack may be for receiving andtransmitting network packet on a first network, and another networkstack for receiving and transmitting network packets on a secondnetwork. In one embodiment, the network stack 267 comprises a buffer 243for queuing one or more network packets for transmission by theappliance 200.

As shown in FIG. 2, the kernel space 204 includes the cache manager 232,a high-speed layer 2-7 integrated packet engine 240, an encryptionengine 234, a policy engine 236 and multi-protocol compression logic238. Running these components or processes 232, 240, 234, 236 and 238 inkernel space 204 or kernel mode instead of the user space 202 improvesthe performance of each of these components, alone and in combination.Kernel operation means that these components or processes 232, 240, 234,236 and 238 run in the core address space of the operating system of thedevice 200. For example, running the encryption engine 234 in kernelmode improves encryption performance by moving encryption and decryptionoperations to the kernel, thereby reducing the number of transitionsbetween the memory space or a kernel thread in kernel mode and thememory space or a thread in user mode. For example, data obtained inkernel mode may not need to be passed or copied to a process or threadrunning in user mode, such as from a kernel level data structure to auser level data structure. In another aspect, the number of contextswitches between kernel mode and user mode are also reduced.Additionally, synchronization of and communications between any of thecomponents or processes 232, 240, 235, 236 and 238 can be performed moreefficiently in the kernel space 204.

In some embodiments, any portion of the components 232, 240, 234, 236and 238 may run or operate in the kernel space 204, while other portionsof these components 232, 240, 234, 236 and 238 may run or operate inuser space 202. In one embodiment, the appliance 200 uses a kernel-leveldata structure providing access to any portion of one or more networkpackets, for example, a network packet comprising a request from aclient 102 or a response from a server 106. In some embodiments, thekernel-level data structure may be obtained by the packet engine 240 viaa transport layer driver interface or filter to the network stack 267.The kernel-level data structure may comprise any interface and/or dataaccessible via the kernel space 204 related to the network stack 267,network traffic or packets received or transmitted by the network stack267. In other embodiments, the kernel-level data structure may be usedby any of the components or processes 232, 240, 234, 236 and 238 toperform the desired operation of the component or process. In oneembodiment, a component 232, 240, 234, 236 and 238 is running in kernelmode 204 when using the kernel-level data structure, while in anotherembodiment, the component 232, 240, 234, 236 and 238 is running in usermode when using the kernel-level data structure. In some embodiments,the kernel-level data structure may be copied or passed to a secondkernel-level data structure, or any desired user-level data structure.

The cache manager 232 may comprise software, hardware or any combinationof software and hardware to provide cache access, control and managementof any type and form of content, such as objects or dynamicallygenerated objects served by the originating servers 106. The data,objects or content processed and stored by the cache manager 232 maycomprise data in any format, such as a markup language, or communicatedvia any protocol. In some embodiments, the cache manager 232 duplicatesoriginal data stored elsewhere or data previously computed, generated ortransmitted, in which the original data may require longer access timeto fetch, compute or otherwise obtain relative to reading a cache memoryelement. Once the data is stored in the cache memory element, future usecan be made by accessing the cached copy rather than refetching orrecomputing the original data, thereby reducing the access time. In someembodiments, the cache memory element nat comprise a data object inmemory 264 of device 200. In other embodiments, the cache memory elementmay comprise memory having a faster access time than memory 264. Inanother embodiment, the cache memory element may comprise any type andform of storage element of the device 200, such as a portion of a harddisk. In some embodiments, the processing unit 262 may provide cachememory for use by the cache manager 232. In yet further embodiments, thecache manager 232 may use any portion and combination of memory,storage, or the processing unit for caching data, objects, and othercontent.

Furthermore, the cache manager 232 includes any logic, functions, rules,or operations to perform any embodiments of the techniques of theappliance 200 described herein. For example, the cache manager 232includes logic or functionality to invalidate objects based on theexpiration of an invalidation time period or upon receipt of aninvalidation command from a client 102 or server 106. In someembodiments, the cache manager 232 may operate as a program, service,process or task executing in the kernel space 204, and in otherembodiments, in the user space 202. In one embodiment, a first portionof the cache manager 232 executes in the user space 202 while a secondportion executes in the kernel space 204. In some embodiments, the cachemanager 232 can comprise any type of general purpose processor (GPP), orany other type of integrated circuit, such as a Field Programmable GateArray (FPGA), Programmable Logic Device (PLD), or Application SpecificIntegrated Circuit (ASIC).

The policy engine 236 may include, for example, an intelligentstatistical engine or other programmable application(s). In oneembodiment, the policy engine 236 provides a configuration mechanism toallow a user to identifying, specify, define or configure a cachingpolicy. Policy engine 236, in some embodiments, also has access tomemory to support data structures such as lookup tables or hash tablesto enable user-selected caching policy decisions. In other embodiments,the policy engine 236 may comprise any logic, rules, functions oroperations to determine and provide access, control and management ofobjects, data or content being cached by the appliance 200 in additionto access, control and management of security, network traffic, networkaccess, compression or any other function or operation performed by theappliance 200. Further examples of specific caching policies are furtherdescribed herein.

The encryption engine 234 comprises any logic, business rules, functionsor operations for handling the processing of any security relatedprotocol, such as SSL or TLS, or any function related thereto. Forexample, the encryption engine 234 encrypts and decrypts networkpackets, or any portion thereof, communicated via the appliance 200. Theencryption engine 234 may also setup or establish SSL or TLS connectionson behalf of the client 102 a-102 n, server 106 a-106 n, or appliance200. As such, the encryption engine 234 provides offloading andacceleration of SSL processing. In one embodiment, the encryption engine234 uses a tunneling protocol to provide a virtual private networkbetween a client 102 a-102 n and a server 106 a-106 n. In someembodiments, the encryption engine 234 is in communication with theEncryption processor 260. In other embodiments, the encryption engine234 comprises executable instructions running on the Encryptionprocessor 260.

The multi-protocol compression engine 238 comprises any logic, businessrules, function or operations for compressing one or more protocols of anetwork packet, such as any of the protocols used by the network stack267 of the device 200. In one embodiment, multi-protocol compressionengine 238 compresses bi-directionally between clients 102 a-102 n andservers 106 a-106 n any TCP/IP based protocol, including MessagingApplication Programming Interface (MAPI) (email), File Transfer Protocol(FTP), HyperText Transfer Protocol (HTTP), Common Internet File System(CIFS) protocol (file transfer), Independent Computing Architecture(ICA) protocol, Remote Desktop Protocol (RDP), Wireless ApplicationProtocol (WAP), Mobile IP protocol, and Voice Over IP (VoIP) protocol.In other embodiments, multi-protocol compression engine 238 providescompression of Hypertext Markup Language (HTML) based protocols and insome embodiments, provides compression of any markup languages, such asthe Extensible Markup Language (XML). In one embodiment, themulti-protocol compression engine 238 provides compression of anyhigh-performance protocol, such as any protocol designed for appliance200 to appliance 200 communications. In another embodiment, themulti-protocol compression engine 238 compresses any payload of or anycommunication using a modified transport control protocol, such asTransaction TCP (T/TCP), TCP with selection acknowledgements (TCP-SACK),TCP with large windows (TCP-LW), a congestion prediction protocol suchas the TCP-Vegas protocol, and a TCP spoofing protocol.

As such, the multi-protocol compression engine 238 acceleratesperformance for users accessing applications via desktop clients, e.g.,Microsoft Outlook and non-Web thin clients, such as any client launchedby popular enterprise applications like Oracle, SAP and Siebel, and evenmobile clients, such as the Pocket PC. In some embodiments, themulti-protocol compression engine 238 by executing in the kernel mode204 and integrating with packet processing engine 240 accessing thenetwork stack 267 is able to compress any of the protocols carried bythe TCP/IP protocol, such as any application layer protocol.

High speed layer 2-7 integrated packet engine 240, also generallyreferred to as a packet processing engine or packet engine, isresponsible for managing the kernel-level processing of packets receivedand transmitted by appliance 200 via network ports 266. The high speedlayer 2-7 integrated packet engine 240 may comprise a buffer for queuingone or more network packets during processing, such as for receipt of anetwork packet or transmission of a network packer. Additionally, thehigh speed layer 2-7 integrated packet engine 240 is in communicationwith one or more network stacks 267 to send and receive network packetsvia network ports 266. The high speed layer 2-7 integrated packet engine240 works in conjunction with encryption engine 234, cache manager 232,policy engine 236 and multi-protocol compression logic 238. Inparticular, encryption engine 234 is configured to perform SSLprocessing of packets, policy engine 236 is configured to performfunctions related to traffic management such as request-level contentswitching and request-level cache redirection, and multi-protocolcompression logic 238 is configured to perform functions related tocompression and decompression of data.

The high speed layer 2-7 integrated packet engine 240 includes a packetprocessing timer 242. In one embodiment, the packet processing timer 242provides one or more time intervals to trigger the processing ofincoming, i.e., received, or outgoing, i.e., transmitted, networkpackets. In some embodiments, the high speed layer 2-7 integrated packetengine 240 processes network packets responsive to the timer 242. Thepacket processing timer 242 provides any type and form of signal to thepacket engine 240 to notify, trigger, or communicate a time relatedevent, interval or occurrence. In many embodiments, the packetprocessing timer 242 operates in the order of milliseconds, such as forexample 100 ms, 50 ms or 25 ms. For example, in some embodiments, thepacket processing timer 242 provides time intervals or otherwise causesa network packet to be processed by the high speed layer 2-7 integratedpacket engine 240 at a 10 ms time interval, while in other embodiments,at a 5 ms time interval, and still yet in further embodiments, as shortas a 3, 2, or 1 ms time interval. The high speed layer 2-7 integratedpacket engine 240 may be interfaced, integrated or in communication withthe encryption engine 234, cache manager 232, policy engine 236 andmulti-protocol compression engine 238 during operation. As such, any ofthe logic, functions, or operations of the encryption engine 234, cachemanager 232, policy engine 236 and multi-protocol compression logic 238may be performed responsive to the packet processing timer 242 and/orthe packet engine 240. Therefore, any of the logic, functions, oroperations of the encryption engine 234, cache manager 232, policyengine 236 and multi-protocol compression logic 238 may be performed atthe granularity of time intervals provided via the packet processingtimer 242, for example, at a time interval of less than or equal to 10ms. For example, in one embodiment, the cache manager 232 may performinvalidation of any cached objects responsive to the high speed layer2-7 integrated packet engine 240 and/or the packet processing timer 242.In another embodiment, the expiry or invalidation time of a cachedobject can be set to the same order of granularity as the time intervalof the packet processing timer 242, such as at every 10 ms.

In contrast to kernel space 204, user space 202 is the memory area orportion of the operating system used by user mode applications orprograms otherwise running in user mode. A user mode application may notaccess kernel space 204 directly and uses service calls in order toaccess kernel services. As shown in FIG. 2, user space 202 of appliance200 includes a graphical user interface (GUI) 210, a command lineinterface (CLI) 212, shell services 214, health monitoring program 216,and daemon services 218. GUI 210 and CLI 212 provide a means by which asystem administrator or other user can interact with and control theoperation of appliance 200, such as via the operating system of theappliance 200 and either is user space 202 or kernel space 204. The GUI210 may be any type and form of graphical user interface and may bepresented via text, graphical or otherwise, by any type of program orapplication, such as a browser. The CLI 212 may be any type and form ofcommand line or text-based interface, such as a command line provided bythe operating system. For example, the CLI 212 may comprise a shell,which is a tool to enable users to interact with the operating system.In some embodiments, the CLI 212 may be provided via a bash, csh, tcsh,or ksh type shell. The shell services 214 comprises the programs,services, tasks, processes or executable instructions to supportinteraction with the appliance 200 or operating system by a user via theGUI 210 and/or CLI 212.

Health monitoring program 216 is used to monitor, check, report andensure that network systems are functioning properly and that users arereceiving requested content over a network. Health monitoring program216 comprises one or more programs, services, tasks, processes orexecutable instructions to provide logic, rules, functions or operationsfor monitoring any activity of the appliance 200. In some embodiments,the health monitoring program 216 intercepts and inspects any networktraffic passed via the appliance 200. In other embodiments, the healthmonitoring program 216 interfaces by any suitable means and/ormechanisms with one or more of the following: the encryption engine 234,cache manager 232, policy engine 236, multi-protocol compression logic238, packet engine 240, daemon services 218, and shell services 214. Assuch, the health monitoring program 216 may call any applicationprogramming interface (API) to determine a state, status, or health ofany portion of the appliance 200. For example, the health monitoringprogram 216 may ping or send a status inquiry on a periodic basis tocheck if a program, process, service or task is active and currentlyrunning. In another example, the health monitoring program 216 may checkany status, error or history logs provided by any program, process,service or task to determine any condition, status or error with anyportion of the appliance 200.

Daemon services 218 are programs that run continuously or in thebackground and handle periodic service requests received by appliance200. In some embodiments, a daemon service may forward the requests toother programs or processes, such as another daemon service 218 asappropriate. As known to those skilled in the art, a daemon service 218may run unattended to perform continuous or periodic system widefunctions, such as network control, or to perform any desired task. Insome embodiments, one or more daemon services 218 run in the user space202, while in other embodiments, one or more daemon services 218 run inthe kernel space.

Referring now to FIG. 2B, another embodiment of the appliance 200 isdepicted. In brief overview, the appliance 200 provides one or more ofthe following services, functionality or operations: SSL VPNconnectivity 280, switching/load balancing 284, Domain Name Serviceresolution 286, acceleration 288 and an application firewall 290 forcommunications between one or more clients 102 and one or more servers106. In one embodiment, the appliance 200 comprises any of the networkdevices manufactured by Citrix Systems, Inc. of Ft. Lauderdale Fla.,referred to as Citrix NetScaler devices. Each of the servers 106 mayprovide one or more network related services 270 a-270 n (referred to asservices 270). For example, a server 106 may provide an http service270. The appliance 200 comprises one or more virtual servers or virtualinternet protocol servers, referred to as a vServer, VIP server, or justVIP 275 a-275 n (also referred herein as vServer 275). The vServer 275receives, intercepts or otherwise processes communications between aclient 102 and a server 106 in accordance with the configuration andoperations of the appliance 200.

The vServer 275 may comprise software, hardware or any combination ofsoftware and hardware. The vServer 275 may comprise any type and form ofprogram, service, task, process or executable instructions operating inuser mode 202, kernel mode 204 or any combination thereof in theappliance 200. The vServer 275 includes any logic, functions, rules, oroperations to perform any embodiments of the techniques describedherein, such as SSL VPN 280, switching/load balancing 284, Domain NameService resolution 286, acceleration 288 and an application firewall290. In some embodiments, the vServer 275 establishes a connection to aservice 270 of a server 106. The service 275 may comprise any program,application, process, task or set of executable instructions capable ofconnecting to and communicating to the appliance 200, client 102 orvServer 275. For example, the service 275 may comprise a web server,http server, ftp, email or database server. In some embodiments, theservice 270 is a daemon process or network driver for listening,receiving and/or sending communications for an application, such asemail, database or an enterprise application. In some embodiments, theservice 270 may communicate on a specific IP address, or IP address andport.

In some embodiments, the vServer 275 applies one or more policies of thepolicy engine 236 to network communications between the client 102 andserver 106. In one embodiment, the policies are associated with aVServer 275. In another embodiment, the policies are based on a user, ora group of users. In yet another embodiment, a policy is global andapplies to one or more vServers 275 a-275 n, and any user or group ofusers communicating via the appliance 200. In some embodiments, thepolicies of the policy engine have conditions upon which the policy isapplied based on any content of the communication, such as internetprotocol address, port, protocol type, header or fields in a packet, orthe context of the communication, such as user, group of the user,vServer 275, transport layer connection, and/or identification orattributes of the client 102 or server 106.

In other embodiments, the appliance 200 communicates or interfaces withthe policy engine 236 to determine authentication and/or authorizationof a remote user or a remote client 102 to access the computingenvironment 15, application, and/or data file from a server 106. Inanother embodiment, the appliance 200 communicates or interfaces withthe policy engine 236 to determine authentication and/or authorizationof a remote user or a remote client 102 to have the application deliverysystem 190 deliver one or more of the computing environment 15,application, and/or data file. In yet another embodiment, the appliance200 establishes a VPN or SSL VPN connection based on the policy engine's236 authentication and/or authorization of a remote user or a remoteclient 103 In one embodiment, the appliance 102 controls the flow ofnetwork traffic and communication sessions based on policies of thepolicy engine 236. For example, the appliance 200 may control the accessto a computing environment 15, application or data file based on thepolicy engine 236.

In some embodiments, the vServer 275 establishes a transport layerconnection, such as a TCP or UDP connection with a client 102 via theclient agent 120. In one embodiment, the vServer 275 listens for andreceives communications from the client 102. In other embodiments, thevServer 275 establishes a transport layer connection, such as a TCP orUDP connection with a client server 106. In one embodiment, the vServer275 establishes the transport layer connection to an internet protocoladdress and port of a server 270 running on the server 106. In anotherembodiment, the vServer 275 associates a first transport layerconnection to a client 102 with a second transport layer connection tothe server 106. In some embodiments, a vServer 275 establishes a pool oftranport layer connections to a server 106 and multiplexes clientrequests via the pooled transport layer connections.

In some embodiments, the appliance 200 provides a SSL VPN connection 280between a client 102 and a server 106. For example, a client 102 on afirst network 102 requests to establish a connection to a server 106 ona second network 104′. In some embodiments, the second network 104′ isnot routable from the first network 104. In other embodiments, theclient 102 is on a public network 104 and the server 106 is on a privatenetwork 104′, such as a corporate network. In one embodiment, the clientagent 120 intercepts communications of the client 102 on the firstnetwork 104, encrypts the communications, and transmits thecommunications via a first transport layer connection to the appliance200. The appliance 200 associates the first transport layer connectionon the first network 104 to a second transport layer connection to theserver 106 on the second network 104. The appliance 200 receives theintercepted communication from the client agent 102, decrypts thecommunications, and transmits the communication to the server 106 on thesecond network 104 via the second transport layer connection. The secondtransport layer connection may be a pooled transport layer connection.As such, the appliance 200 provides an end-to-end secure transport layerconnection for the client 102 between the two networks 104, 104′.

In one embodiment, the appliance 200 hosts an intranet internet protocolor intranetIP 282 address of the client 102 on the virtual privatenetwork 104. The client 102 has a local network identifier, such as aninternet protocol (IP) address and/or host name on the first network104. When connected to the second network 104′ via the appliance 200,the appliance 200 establishes, assigns or otherwise provides anIntranetIP, which is network identifier, such as IP address and/or hostname, for the client 102 on the second network 104′. The appliance 200listens for and receives on the second or private network 104′ for anycommunications directed towards the client 102 using the client'sestablished IntranetIP 282. In one embodiment, the appliance 200 acts asor on behalf of the client 102 on the second private network 104. Forexample, in another embodiment, a vServer 275 listens for and respondsto communications to the IntranetIP 282 of the client 102. In someembodiments, if a computing device 100 on the second network 104′transmits a request, the appliance 200 processes the request as if itwere the client 102. For example, the appliance 200 may respond to aping to the client's IntranetIP 282. In another example, the appliancemay establish a connection, such as a TCP or UDP connection, withcomputing device 100 on the second network 104 requesting a connectionwith the client's IntranetIP 282.

In some embodiments, the appliance 200 provides one or more of thefollowing acceleration techniques 288 to communications between theclient 102 and server 106: 1) compression; 2) decompression; 3)Transmission Control Protocol pooling; 4) Transmission Control Protocolmultiplexing; 5) Transmission Control Protocol buffering; and 6)caching. In one embodiment, the appliance 200 relieves servers 106 ofmuch of the processing load caused by repeatedly opening and closingtransport layers connections to clients 102 by opening one or moretransport layer connections with each server 106 and maintaining theseconnections to allow repeated data accesses by clients via the Internet.This technique is referred to herein as “connection pooling”.

In some embodiments, in order to seamlessly splice communications from aclient 102 to a server 106 via a pooled transport layer connection, theappliance 200 translates or multiplexes communications by modifyingsequence number and acknowledgment numbers at the transport layerprotocol level. This is referred to as “connection multiplexing”. Insome embodiments, no application layer protocol interaction is required.For example, in the case of an in-bound packet (that is, a packetreceived from a client 102), the source network address of the packet ischanged to that of an output port of appliance 200, and the destinationnetwork address is changed to that of the intended server. In the caseof an outbound packet (that is, one received from a server 106), thesource network address is changed from that of the server 106 to that ofan output port of appliance 200 and the destination address is changedfrom that of appliance 200 to that of the requesting client 102. Thesequence numbers and acknowledgment numbers of the packet are alsotranslated to sequence numbers and acknowledgement expected by theclient 102 on the appliance's 200 transport layer connection to theclient 102. In some embodiments, the packet checksum of the transportlayer protocol is recalculated to account for these translations.

In another embodiment, the appliance 200 provides switching orload-balancing functionality 284 for communications between the client102 and server 106. In some embodiments, the appliance 200 distributestraffic and directs client requests to a server 106 based on layer 4 orapplication-layer request data. In one embodiment, although the networklayer or layer 2 of the network packet identifies a destination server106, the appliance 200 determines the server 106 to distribute thenetwork packet by application information and data carried as payload ofthe transport layer packet. In one embodiment, the health monitoringprograms 216 of the appliance 200 monitor the health of servers todetermine the server 106 for which to distribute a client's request. Insome embodiments, if the appliance 200 detects a server 106 is notavailable or has a load over a predetermined threshold, the appliance200 can direct or distribute client requests to another server 106.

In some embodiments, the appliance 200 acts as a Domain Name Service(DNS) resolver or otherwise provides resolution of a DNS request fromclients 102. In some embodiments, the appliance intercepts' a DNSrequest transmitted by the client 102. In one embodiment, the appliance200 responds to a client's DNS request with an IP address of or hostedby the appliance 200. In this embodiment, the client 102 transmitsnetwork communication for the domain name to the appliance 200. Inanother embodiment, the appliance 200 responds to a client's DNS requestwith an IP address of or hosted by a second appliance 200′. In someembodiments, the appliance 200 responds to a client's DNS request withan IP address of a server 106 determined by the appliance 200.

In yet another embodiment, the appliance 200 provides applicationfirewall functionality 290 for communications between the client 102 andserver 106. In one embodiment, the policy engine 236 provides rules fordetecting and blocking illegitimate requests. In some embodiments, theapplication firewall 290 protects against denial of service (DoS)attacks. In other embodiments, the appliance inspects the content ofintercepted requests to identify and block application-based attacks. Insome embodiments, the rules/policy engine 236 comprises one or moreapplication firewall or security control policies for providingprotections against various classes and types of web or Internet basedvulnerabilities, such as one or more of the following: 1) bufferoverflow, 2) CGI-BIN parameter manipulation, 3) form/hidden fieldmanipulation, 4) forceful browsing, 5) cookie or session poisoning, 6)broken access control list (ACLs) or weak passwords, 7) cross-sitescripting (XSS), 8) command injection, 9) SQL injection, 10) errortriggering sensitive information leak, 11) insecure use of cryptography,12) server misconfiguration, 13) back doors and debug options, 14)website defacement, 15) platform or operating systems vulnerabilities,and 16) zero-day exploits. In an embodiment, the application firewall290 provides HTML form field protection in the form of inspecting oranalyzing the network communication for one or more of the following: 1)required fields are returned, 2) no added field allowed, 3) read-onlyand hidden field enforcement, 4) drop-down list and radio button fieldconformance, and 5) form-field max-length enforcement. In someembodiments, the application firewall 290 ensures cookies are notmodified. In other embodiments, the application firewall 290 protectsagainst forceful browsing by enforcing legal URLs.

In still yet other embodiments, the application firewall 290 protectsany confidential information contained in the network communication. Theapplication firewall 290 may inspect or analyze any networkcommunication in accordance with the rules or polices of the engine 236to identify any confidential information in any field of the networkpacket. In some embodiments, the application firewall 290 identifies inthe network communication one or more occurrences of a credit cardnumber, password, social security number, name, patient code, contactinformation, and age. The encoded portion of the network communicationmay comprise these occurrences or the confidential information. Based onthese occurrences, in one embodiment, the application firewall 290 maytake a policy action on the network communication, such as preventtransmission of the network communication. In another embodiment, theapplication firewall 290 may rewrite, remove or otherwise mask suchidentified occurrence or confidential information.

C. Client Agent

Referring now to FIG. 3, an embodiment of the client agent 120 isdepicted. The client 102 includes a client agent 120 for establishingand exchanging communications with the appliance 200 and/or server 106via a network 104. In brief overview, the client 102 operates oncomputing device 100 having an operating system with a kernel mode 302and a user mode 303, and a network stack 310 with one or more layers 310a-310 b. The client 102 may have installed and/or execute one or moreapplications. In some embodiments, one or more applications maycommunicate via the network stack 310 to a network 104. One of theapplications, such as a web browser, may also include a first program322. For example, the first program 322 may be used in some embodimentsto install and/or execute the client agent 120, or any portion thereof.The client agent 120 includes an interception mechanism, or interceptor350, for intercepting network communications from the network stack 310from the one or more applications.

The network stack 310 of the client 102 may comprise any type and formof software, or hardware, or any combinations thereof, for providingconnectivity to and communications with a network. In one embodiment,the network stack 310 comprises a software implementation for a networkprotocol suite. The network stack 310 may comprise one or more networklayers, such as any networks layers of the Open Systems Interconnection(OSI) communications model as those skilled in the art recognize andappreciate. As such, the network stack 310 may comprise any type andform of protocols for any of the following layers of the OSI model: 1)physical link layer, 2) data link layer, 3) network layer, 4) transportlayer, 5) session layer, 6) presentation layer, and 7) applicationlayer. In one embodiment, the network stack 310 may comprise a transportcontrol protocol (TCP) over the network layer protocol of the internetprotocol (IP), generally referred to as TCP/IP. In some embodiments, theTCP/IP protocol may be carried over the Ethernet protocol, which maycomprise any of the family of IEEE wide-area-network (WAN) orlocal-area-network (LAN) protocols, such as those protocols covered bythe IEEE 802.3. In some embodiments, the network stack 310 comprises anytype and form of a wireless protocol, such as IEEE 802.11 and/or mobileinternet protocol.

In view of a TCP/IP based network, any TCP/IP based protocol may beused, including Messaging Application Programming Interface (MAPI)(email), File Transfer Protocol (FTP), HyperText Transfer Protocol(HTTP), Common Internet File System (CIFS) protocol (file transfer),Independent Computing Architecture (ICA) protocol, Remote DesktopProtocol (RDP), Wireless Application Protocol (WAP), Mobile IP protocol,and Voice Over IP (VoIP) protocol. In another embodiment, the networkstack 310 comprises any type and form of transport control protocol,such as a modified transport control protocol, for example a TransactionTCP (T/TCP), TCP with selection acknowledgements (TCP-SACK), TCP withlarge windows (TCP-LW), a congestion prediction protocol such as theTCP-Vegas protocol, and a TCP spoofing protocol. In other embodiments,any type and form of user datagram protocol (UDP), such as UDP over IP,may be used by the network stack 310, such as for voice communicationsor real-time data communications.

Furthermore, the network stack 310 may include one or more networkdrivers supporting the one or more layers, such as a TCP driver or anetwork layer driver. The network drivers may be included as part of theoperating system of the computing device 100 or as part of any networkinterface cards or other network access components of the computingdevice 100. In some embodiments, any of the network drivers of thenetwork stack 310 may be customized, modified or adapted to provide acustom or modified portion of the network stack 310 in support of any ofthe techniques described herein. In other embodiments, the accelerationprogram 120 is designed and constructed to operate with or work inconjunction with the network stack 310 installed or otherwise providedby the operating system of the client 102.

The network stack 310 comprises any type and form of interfaces forreceiving, obtaining, providing or otherwise accessing any informationand data related to network communications of the client 102. In oneembodiment, an interface to the network stack 310 comprises anapplication programming interface (API). The interface may also compriseany function call, hooking or filtering mechanism, event or call backmechanism, or any type of interfacing technique. The network stack 310via the interface may receive or provide any type and form of datastructure, such as an object, related to functionality or operation ofthe network stack 3 10. For example, the data structure may compriseinformation and data related to a network packet or one or more networkpackets. In some embodiments, the data structure comprises a portion ofthe network packet processed at a protocol layer of the network stack310, such as a network packet of the transport layer. In someembodiments, the data structure 325 comprises a kernel-level datastructure, while in other embodiments, the data structure 325 comprisesa user-mode data structure. A kernel-level data structure may comprise adata structure obtained or related to a portion of the network stack 310operating in kernel-mode 302, or a network driver or other softwarerunning in kernel-mode 302, or any data structure obtained or receivedby a service, process, task, thread or other executable instructionsrunning or operating in kernel-mode of the operating system.

Additionally, some portions of the network stack 310 may execute oroperate in kernel-mode 302, for example, the data link or network layer,while other portions execute or operate in user-mode 303, such as anapplication layer of the network stack 310. For example, a first portion310 a of the network stack may provide user-mode access to the networkstack 310 to an application while a second portion 310 a of the networkstack 310 provides access to a network. In some embodiments, a firstportion 310 a of the network stack may comprise one or more upper layersof the network stack 310, such as any of layers 5-7. In otherembodiments, a second portion 310 b of the network stack 310 comprisesone or more lower layers, such as any of layers 1-4. Each of the firstportion 310 a and second portion 310 b of the network stack 310 maycomprise any portion of the network stack 310, at any one or morenetwork layers, in user-mode 203, kernel-mode, 202, or combinationsthereof, or at any portion of a network layer or interface point to anetwork layer or any portion of or interface point to the user-mode 203and kernel-mode 203.

The interceptor 350 may comprise software, hardware, or any combinationof software and hardware. In one embodiment, the interceptor 350intercept a network communication at any point in the network stack 310,and redirects or transmits the network communication to a destinationdesired, managed or controlled by the interceptor 350 or client agent120. For example, the interceptor 350 may intercept a networkcommunication of a network stack 310 of a first network and transmit thenetwork communication to the appliance 200 for transmission on a secondnetwork 104. In some embodiments, the interceptor 350 comprises any typeinterceptor 350 comprises a driver, such as a network driver constructedand designed to interface and work with the network stack 310. In someembodiments, the client agent 120 and/or interceptor 350 operates at oneor more layers of the network stack 310, such as at the transport layer.In one embodiment, the interceptor 350 comprises a filter driver,hooking mechanism, or any form and type of suitable network driverinterface that interfaces to the transport layer of the network stack,such as via the transport driver interface (TDI). In some embodiments,the interceptor 350 interfaces to a first protocol layer, such as thetransport layer and another protocol layer, such as any layer above thetransport protocol layer, for example, an application protocol layer. Inone embodiment, the interceptor 350 may comprise a driver complying withthe Network Driver Interface Specification (NDIS), or a NDIS driver. Inanother embodiment, the interceptor 350 may comprise a min-filter or amini-port driver. In one embodiment, the interceptor 350, or portionthereof, operates in kernel-mode 202. In another embodiment, theinterceptor 350, or portion thereof, operates in user-mode 203. In someembodiments, a portion of the interceptor 350 operates in kernel-mode202 while another portion of the interceptor 350 operates in user-mode203. In other embodiments, the client agent 120 operates in user-mode203 but interfaces via the interceptor 350 to a kernel-mode driver,process, service, task or portion of the operating system, such as toobtain a kernel-level data structure 225. In further embodiments, theinterceptor 350 is a user-mode application or program, such asapplication.

In one embodiment, the interceptor 350 intercepts any transport layerconnection requests. In these embodiments, the interceptor 350 executetransport layer application programming interface (API) calls to set thedestination information, such as destination IP address and/or port to adesired location for the location. In this manner, the interceptor 350intercepts and redirects the transport layer connection to a IP addressand port controlled or managed by the interceptor 350 or client agent120. In one embodiment, the interceptor 350 sets the destinationinformation for the connection to a local IP address and port of theclient 102 on which the client agent 120 is listening. For example, theclient agent 120 may comprise a proxy service listening on a local IPaddress and port for redirected transport layer communications. In someembodiments, the client agent 120 then communicates the redirectedtransport layer communication to the appliance 200.

In some embodiments, the interceptor 350 intercepts a Domain NameService (DNS) request. In one embodiment, the client agent 120 and/orinterceptor 350 resolves the DNS request. In another embodiment, theinterceptor transmits the intercepted DNS request to the appliance 200for DNS resolution. In one embodiment, the appliance 200 resolves theDNS request and communicates the DNS response to the client agent 120.In some embodiments, the appliance 200 resolves the DNS request viaanother appliance 200′ or a DNS server 106.

In yet another embodiment, the client agent 120 may comprise two agents120 and 120′. In one embodiment, a first agent 120 may comprise aninterceptor 350 operating at the network layer of the network stack 310.In some embodiments, the first agent 120 intercepts network layerrequests such as Internet Control Message Protocol (ICMP) requests(e.g., ping and traceroute). In other embodiments, the second agent 120′may operate at the transport layer and intercept transport layercommunications. In some embodiments, the first agent 120 interceptscommunications at one layer of the network stack 210 and interfaces withor communicates the intercepted communication to the second agent 120′.

The client agent 120 and/or interceptor 350 may operate at or interfacewith a protocol layer in a manner transparent to any other protocollayer of the network stack 310. For example, in one embodiment, theinterceptor 350 operates or interfaces with the transport layer of thenetwork stack 310 transparently to any protocol layer below thetransport layer, such as the network layer, and any protocol layer abovethe transport layer, such as the session, presentation or applicationlayer protocols. This allows the other protocol layers of the networkstack 310 to operate as desired and without modification for using theinterceptor 350. As such, the client agent 120 and/or interceptor 350can interface with the transport layer to secure, optimize, accelerate,route or load-balance any communications provided via any protocolcarried by the transport layer, such as any application layer protocolover TCP/IP.

Furthermore, the client agent 120 and/or interceptor may operate at orinterface with the network stack 310 in a manner transparent to anyapplication, a user of the client 102, and any other computing device,such as a server, in communications with the client 102. The clientagent 120 and/or interceptor 350 may be installed and/or executed on theclient 102 in a manner without modification of an application. In someembodiments, the user of the client 102 or a computing device incommunications with the client 102 are not aware of the existence,execution or operation of the client agent 120 and/or interceptor 350.As such, in some embodiments, the client agent 120 and/or interceptor350 is installed, executed, and/or operated transparently to anapplication, user of the client 102, another computing device, such as aserver, or any of the protocol layers above and/or below the protocollayer interfaced to by the interceptor 350.

The client agent 120 includes an acceleration program 302, a streamingclient 306, and/or a collection agent 304. In one embodiment, the clientagent 120 comprises an Independent Computing Architecture (ICA) client,or any portion thereof, developed by Citrix Systems, Inc. of FortLauderdale, Fla., and is also referred to as an ICA client. In someembodiments, the client 120 comprises an application streaming client306 for streaming an application from a server 106 to a client 102. Insome embodiments, the client agent 120 comprises an acceleration program302 for accelerating communications between client 102 and server 106.In another embodiment, the client agent 120 includes a collection agent304 for performing end-point detection/scanning and collecting end-pointinformation for the appliance 200 and/or server 106.

In some embodiments, the acceleration program 302 comprises aclient-side acceleration program for performing one or more accelerationtechniques to accelerate, enhance or otherwise improve a client'scommunications with and/or access to a server 106, such as accessing anapplication provided by a server 106. The logic, functions, and/oroperations of the executable instructions of the acceleration program302 may perform one or more of the following acceleration techniques: 1)multi-protocol compression, 2) transport control protocol pooling, 3)transport control protocol multiplexing, 4) transport control protocolbuffering, and 5) caching via a cache manager. Additionally, theacceleration program 302 may perform encryption and/or decryption of anycommunications received and/or transmitted by the client 102. In someembodiments, the acceleration program 302 performs one or more of theacceleration techniques in an integrated manner or fashion.Additionally, the acceleration program 302 can perform compression onany of the protocols, or multiple-protocols, carried as a payload of anetwork packet of the transport layer protocol.

The streaming client 306 comprises an application, program, process,service, task or executable instructions for receiving and executing astreamed application from a server 106. A server 106 may stream one ormore application data files to the streaming client 306 for playing,executing or otherwise causing to be executed the application on theclient 102. In some embodiments, the server 106 transmits a set ofcompressed or packaged application data files to the streaming client306. In some embodiments, the plurality of application files arecompressed and stored on a file server within an archive file such as aCAB, ZIP, SIT, TAR, JAR or other archives In one embodiment, the server106 decompresses, unpackages or unarchives the application files andtransmits the files to the client 102. In another embodiment, the client102 decompresses, unpackages or unarchives the application files. Thestreaming client 306 dynamically installs the application, or portionthereof, and executes the application. In one embodiment, the streamingclient 306 may be an executable program. In some embodiments, thestreaming client 306 may be able to launch another executable program.

The collection agent 304 comprises an application, program, process,service, task or executable instructions for identifying, obtainingand/or collecting information about the client 102. In some embodiments,the appliance 200 transmits the collection agent 304 to the client 102or client agent 120. The collection agent 304 may be configuredaccording to one or more policies of the policy engine 236 of theappliance. In other embodiments, the collection agent 304 transmitscollected information on the client 102 to the appliance 200. In oneembodiment, the policy engine 236 of the appliance 200 uses thecollected information to determine and provide access, authenticationand authorization control of the client's connection to a network 104.

In one embodiment, the collection agent 304 comprises an end-pointdetection and scanning mechanism, which identifies and determines one ormore attributes or characteristics of the client. For example, thecollection agent 304 may identify and determine any one or more of thefollowing client-side attributes: 1) the operating system an/or aversion of an operating system, 2) a service pack of the operatingsystem, 3) a running service, 4) a running process, and 5) a file. Thecollection agent 304 may also identify and determine the presence orversions of any one or more of the following on the client: 1) antivirussoftware, 2) personal firewall software, 3) anti-spam software, and 4)internet security software. The policy engine 236 may have one or morepolicies based on any one or more of the attributes or characteristicsof the client or client-side attributes.

In some embodiments and still referring to FIG. 3, a first program 322may be used to install and/or execute the client agent 120, or portionthereof, such as the interceptor 350, automatically, silently,transparently, or otherwise. In one embodiment, the first program 322comprises a plugin component, such an ActiveX control or Java control orscript that is loaded into and executed by an application. For example,the first program comprises an ActiveX control loaded and run by a webbrowser application, such as in the memory space or context of theapplication. In another embodiment, the first program 322 comprises aset of executable instructions loaded into and run by the application,such as a browser. In one embodiment, the first program 322 comprises adesigned and constructed program to install the client agent 120. Insome embodiments, the first program 322 obtains, downloads, or receivesthe client agent 120 via the network from another computing device. Inanother embodiment, the first program 322 is an installer program or aplug and play manager for installing programs, such as network drivers,on the operating system of the client 102.

D. Fine-Grained Client-Side Interception

Referring now to FIG. 4, an embodiment of a system for providingfine-grained client-side interception is depicted. In one embodiment,the system of FIG. 4 provides a more granular mechanism for interceptingcommunication of a client 102 having an SSL VPN connection to network104′ via the appliance 200. In brief overview, the appliance 200comprises an application routing table 400. The application routingtable (ART) 400 provides a network destination description 410 and/or aclient application identifier 450. In some embodiments, the applicationrouting table 400 via the network destination description identifies theapplications or services 270 on servers 106 which are authorized foraccess by a client 102. In other embodiments, the application routingtable 400 identifies via the client application identifier 450 anapplication running on the client 102 that may be authorized for a levelof access to the server 106, or a service 270 of the server 106. Theappliance 200 may transmit the application routing table 400 to theclient 102 or client agent 120. The client agent 120 uses theapplication routing table 400 to make determination on whether tointercept and transmit client network communication to the appliance200, such as via a SSL VPN tunnel to appliance, based on the applicationrouting table 400.

The application routing table 400 comprises any type and form of table,database, object or data structure for arranging and storing informationas described herein. In some embodiments, the application routing table400 is populated, configured, created, edited or modified via a commandline interface 212 or graphical user interface 210 of the appliance. Inother embodiments, application routing table 400 is populated,configured, created, edited or modified via the client 102, server 106or another computing device 100. In one embodiment, the client 102receives the application routing table 400 from the appliance 200. Forexample, the client agent 120 receives the application routing table 400upon establishing a connection with the appliance 200. In anotherexample, the client agent 120 downloads the application routing table400 from a server, a web-site or any other computing device 100 on thenetwork 104. In another embodiment, a user creates or modifies theapplication routing table 400 on the client 102.

In some embodiments, the application routing table 400 comprises one ormore network destination descriptions 410. The network destinationdescription 410 may comprise information identifying one or more of thefollowing: a destination network identifier 415, a destination port 420,a protocol 425, a source network identifier 430, a source port 435, andan intranet application name 440. The destination network identifier 415and source network identifier 430 may comprise a host or domain name,and/or an internet protocol address. In some embodiments, destinationnetwork identifier 415 and source network identifier 430 comprises arange of internet protocol addresses, a list of internet protocoladdresses and/or a list of domain or host names. The destination port420 and source port 435 identifies one or more port numbers for anetwork communication end-point. For example, the destination port 430may identify port 80 for http traffic an http or web-server. In anotherexample, the destination port 430 may identify port 21 for file transferprotocol (ftp). In some embodiments, the protocol identifier 425identifies one or more types of protocol by name, number, version orapplication. In other embodiment, the protocol identifier 425 identifiesthe protocol by layer of the network stack, such as Layer 1-7. In oneembodiment, the intranet application name 440 identifies a name oridentifier of an application associated with the destination networkidentifier 415 and/or destination port 420. For example, the intranetapplication name 440 may identify a name of the email, database, or acorporate application being accessed via the destination networkidentifier 415 and/or destination port 420.

In one embodiment, the network destination description 410 identifies byinternet protocol layer information or network layer information alocation of an application or service 270 on a network 104. For example,a destination network identifier 415 and destination port 420 mayidentify a destination location of an application on a network 104. Insome embodiments, the network destination description 410 identifies adestination authorized for access via the appliance 200. In anotherembodiment, the network destination description 410 identifies byinternet protocol layer information or network layer information alocation of a client accessing the application or service 270 of aserver 106 via the network 104. For example, a destination networkidentifier 415 and destination port 420 may identify a destinationlocation of an application on a network. In some embodiments, thenetwork destination description 410 identifies a client authorized toaccess the network 104 or server 106 via the appliance 200. In yetanother embodiment, the network destination description identifies byinternet protocol or network layer information the source anddestination of traffic flow between a client 102 and a server 106. Inone embodiment, the network destination description 410 identifies atraffic flow between a client 102 and server 106 authorized for accessvia the appliance 200.

In some embodiments, the application routing table 400 comprises one ormore client application identifiers 450. The client applicationidentifier 450 identifies an application installed or operating on theclient 102 authorized for access to a network 104 or a server 106 viathe appliance 200. In one embodiment, the client application identifier450 comprises a name of an executable file for the application, such athe name of the .exe file of the application. For example, the clientapplication identifier 405 may include the name “explorer.exe”,“outlook.exe” or “winword.exe”. In other embodiments, the clientapplication identifier 450 identifies an image name of a process orexecutable. In another embodiment, the client application identifier 450comprises a name of a script. In yet another embodiment, the clientapplication identifier 450 comprises a name of a process, task orservice that may or is operating on the client 102. In still anotherembodiment, the client application identifier 450 comprises a processidentifier, or PID, or a range of PIDS.

In one embodiment, the policy engine 236 of the appliance 200 comprisesone or more rules associated with the application routing table 400, orany portion thereof. In some embodiments, the policy engine 236comprises a policy for access, authorization, and/or auditing based on anetwork destination description 410. In other embodiments, the policyengine 236 comprises a policy for access, authorization, and/or auditingbased on a client application identifier 450. In another embodiment, thepolicy engine 236 comprises a policy for session and/or trafficmanagement policies based on the network destination description 410and/or client application identifier 450. In yet another embodiment, theclient 102 comprises a policy engine 236 for applying one or morepolicies or rules based on the network destination description 410and/or client application identifier 450.

In operation, the client agent 120 uses the application routing table400 for determining the network communications on the network stack 310to intercept. In one embodiment, the client agent 120 intercepts networkcommunication having information identifying or corresponding to anetwork destination description 410. For example, the client agent 120may intercept a network packet on the network stack 310 destined for adestination network identifier 415 and/or destination port 420 of anetwork destination description 410 of an application routing table 400.In another embodiment, the client agent 120 intercepts networkcommunications on the network stack 310 originating from an applicationon the client 102 corresponding to a client application identifier 450of the application routing table 400. In other embodiments, the clientagent 120 does not intercept network communications on the network stack310 that do not correspond to either a network destination description410 or a client application identifier 450.

Referring now to FIG. 5, an embodiment of a method 500 for a client 102intercepting network communications of the client 102 based on thegranularity specified by the application routing table 400 is depicted.In brief overview, the method 500, at step 505, the client 102establishes a connection with the appliance 200, such as an SSL VPNconnection. At step 510, the client agent 120 receives an applicationrouting table 400 from the appliance 200. At step 515, the client agent120 intercepts a request of the client 102. In one embodiment, theclient agent 120, at step 520, identifies the application originating orgenerating the request. At step 525, the client agent 102 determineswhether to transmit the intercepted request via the connection with theappliance 200 based on the application routing table 400. For example,if the request originates from an application identified by the clientapplication identifier 450, the client agent 120 transmits theintercepted request via the connection to the appliance 200. If, at step530, the client agent 120 determines the intercepted request is allowedaccess to the network 104 via the appliance 200, the client agent 120transmits the intercepted request via the connection to the appliance200. Otherwise, the client agent 120 drops the request or allows it tobe transmitted via the network stack 210 of the client 102.

In further detail, at step 505, the client agent 102 establishes atransport layer connection with the appliance 200, such as via thetransport control protocol or user datagram protocol. In one embodiment,the client agent 120 establishes a tunnel connection with the appliance200 using any type and form of tunneling protocol. In anotherembodiment, the client agent 120 establishes a virtual private networkconnection via the appliance 200 to a network 104. For example, theclient agent 120 may establish a virtual private network connection withthe appliance 200 to connect the client 102 on the first network 104 toa second network 104′. In some embodiments, the client agent 120establishes a SSL VPN connection with the appliance 200. In yet anotherembodiment, the client agent 120 establishes a tunnel or virtual privatenetwork connection using Transport Layer Secure (TLS) protocol. In oneembodiment, the client agent 120 establishes a tunnel connection usingthe Common Gateway Protocol (CGP) manufactured by Citrix Systems, Inc.of Ft. Lauderdale, Fla.

At step 510, the client agent 120 obtains or receives an applicationrouting table 400 from the appliance 200, a user of the client 200, or acomputing device 100. In one embodiment, the client agent 120 receivesthe application routing table 400 upon establishing a connection withthe appliance 200. For example, the client agent 120 may request theapplication routing table 400 from the appliance 200. In anotherembodiment, the appliance 400 transmits the application routing table400 to the client agent 120. For example, if a change to the applicationrouting table 400 is made, the appliance 200 may transmit or push thechanges to the client agent 120. In some embodiments, the client agent120 loads or opens the application routing table 400 from storage on theclient 120 or a computing device 100 accessible via the network 104. Inyet another embodiment, the client agent 120 downloads the applicationrouting table 400 from a web-site, such as via http. In a furtherembodiment, the client agent 120 transfer a file having the applicationrouting table 400 via a file transfer protocol (FTP). In one embodiment,a user creates or generates the application routing table on the client120. In another embodiment, a user configures the client agent 120 tohave the application routing table 400.

At step 515, the client agent 120 intercepts on the network stack 310 arequest of the client 102. In one embodiment, the client agent 120intercepts a request to open a transport layer connection from anapplication on the client 102. In another embodiment, the client agent120 intercepts a request of an application for an established transportlayer connection. In some embodiments, the client agent 120 intercepts anetwork packet destined for the first network 104 of the client 102. Inanother embodiment, the client agent 120 intercepts a network packetdestined for a second network 104 provided by a VPN connection to theappliance 200. In one embodiment, the client agent 120 intercepts atransport layer network packet at an interface at the transport layer ofthe network stack 310, such as via the transport driver interface (TDI).In other embodiments, the client agent 120 intercepts a network packetat any layer at or below the transport layer or layer 4 of the networkstack 210, such as the network or IP layer. In still another embodiment,the client agent 120 intercepts a network packet at layer 4 and above,such as the application layer of the network stack 310.

In some embodiments, the client agent 120, at step 520 identifies anapplication generating or originating the intercepted request by anysuitable means and/or mechanism. In one embodiment, the client agent 120determines an identifier of the application via a system level orkernel-mode function call. In one embodiment, the client 120 determinesvia an application programming interface (API) the process id (PID)and/or the name of the application associated with the connection orcontext from which the request was intercepted. In some embodiments, theclient agent 120 determines an identifier of the application at the timethe client agent 120 intercepts the application's connection request viathe network stack 210. In other embodiments, the client agent 120determines an identifier of the application via inspection of a payloadof the intercepted request. In one embodiment, the client agent 120stores the application identifier in a storage, such as a datastructure, object, table, file or database. In another embodiment, theclient 120 associates or maintains an associations of an identifier ofthe application with a transport layer connection of the application,such as the transport layer connection established via the client agent120 to the appliance 200.

At step 525, the client agent 102 uses the application routing table 400to determine which network communications of the client 102 to interceptand transmit via the established connection with the appliance 200. Insome embodiments, the client agent 120 intercepts network communicationsof the client 120 on a first network 104 and transmit via a transportlayer connection or application layer protocol to a second network 104′via the appliance 200. By intercepting only those network communicationsof the client corresponding to a network destination description 410and/or client application identifier 450 of the application routingtable 400, the client agent 120 provides a more secure mechanism andfiner grain control of transmitting network communications via thetunnel or connection to the second network 104′. In one embodiment, theclient agent 120 inspects or analyzes the intercepted request todetermine one or more of the following information: destination IPaddress, destination port, source IP address, and source port. In someembodiments, the client agent 120 obtains any of the network layer or IPrelated information of the network packet of the request.

In one embodiment, the client agent 120 compares the information of theintercepted request with the network destination description 410 of theapplication routing table 400. If the intercepted request matches thenetwork destination description 410, the client agent 120 transmits, atstep 430, the intercepted request via the connection to the appliance200. In other embodiments, if the intercepted request does notcorrespond to a network destination description 410, the client agent120, at step 435, does not transmit the intercepted request via theconnection to the appliance 200. In some embodiments, the client agent120 drops the intercepted request. In another embodiment, the clientagent 120 does not intercept the request but allows it to pass via thenetwork stack 310 of the client 120. In some cases, the client 102transmits the request via the first network 104 of the client instead ofvia the connection to the appliance 200. In one embodiment, the clientagent 120 determines an identifier of the application from theintercepted request. In some embodiments, the client agent 120 looks upthe application associated with the context or connection of therequest. In another embodiment, the client agent 120 determines a nameand/or PID of the application via a system API call. In someembodiments, the client agent 120 identifies the application frominspection o analysis of the network packet of the request. For example,in one embodiment, the client agent 120 uses information from a payloadof the network packet to identify the application.

In one embodiment, the client agent 120, at step 425, compares theinformation of the intercepted request with the client applicationidentifier 450 of the application routing table 400. If the applicationidentifies as originating or transmitting the intercepted requestmatches the client application identifier 450, the client agent 120transmits, at step 430, the intercepted request via the connection tothe appliance 200. In other embodiments, if the intercepted request doesnot correspond to the client application identifier 450, the clientagent 120 does not transmit the intercepted request via the connectionto the appliance 200. In some embodiments, the client agent 120 dropsthe intercepted request. In another embodiment, the client agent 120does not intercept the request but allows it to pass via the networkstack 310 of the client 120. In some cases, the client 102 transmits therequest via the first network 104 of the client instead of via theconnection to the appliance 200 In some embodiments, the applicationrouting table 400 identifies a network destination description 410and/or client application identifier 450 that the client agent 120should not intercept. As such, in one embodiment, the method 500described above is used to determine which network packets or clientrequests to not transmit via the appliance based on information in theapplication routing table 400. In another embodiment, the client agent120 transmits any network communication of the client 102 or applicationvia the appliance 200 unless it corresponds to a network destinationdescription 410 or client application identifier 450.

With the above described method 500, the client agent 120 intercepts andtransmits those network packets of the client 120 meeting finelycontrolled application descriptions. In this manner and in someembodiments, the client agent 120 and appliance 200 provide a moresecure network tunneling mechanism to connect the client 102 to aprivate network 104′. In one embodiment, the client agent 120 interceptsnetwork packets having certain network layer and routing information andswitches the transmission of the network packet via layer 4 orapplication layer information via a transport layer connection to theappliance 200.

Referring now to FIG. 6, steps of an embodiment of a method 600 aredepicted for applying a policy to control an application's access viathe appliance 200 based on identification of the application. In briefoverview, at step 605, the client agent 102 establishes a connectionwith the appliance 200. At step 610, the client agent 102 intercepts arequest of an application on the client 102, and step 615, identifiesthe application on the client making the request. At step 620, theclient agent 120 transmits an identifier of the application to theappliance 200. At step 625, the client agent 120 transmits anintercepted request of the application to the appliance 200. At step630, the appliance 200 determines a level of access to provide theapplication of the client 102 based on the identification of theapplication and an associated policy. At step 635, in one embodiment,the appliance 200 grants the application a level of access via theappliance to one of a network 104 or server 106. In another embodiment,the appliance 200, at step 640, denies the application a level of accessvia the appliance to the network 104 or server 106.

In further details, at step 605, the client 102, such as via clientagent 120, establishes a connection with the appliance 200. In someembodiments, the client agent 102 establishes a transport layerconnection with the appliance 200, such as via the transport controlprotocol or user datagram protocol. In one embodiment, the client agent120 establishes a tunnel connection with the appliance 200 using anytype and form of tunneling protocol. In another embodiment, the clientagent 120 establishes a virtual private network connection via theappliance 200 to a network 104, such as a SSL VPN or TLS VPN connection.In yet another embodiment, the client agent 120 establishes a tunnelconnection using the Common Gateway Protocol (CGP) manufactured byCitrix Systems, Inc. of Ft. Lauderdale.

At step 610, the client agent 120 intercepts on the network stack 310 arequest of the application. In one embodiment, the client agent 120intercepts a request to open a transport layer connection to a server104 via the appliance 200. In another embodiment, the client agent 120intercepts a request of an application to a server via an establishedtransport layer connection with the appliance 200. In some embodiments,the client agent 120 intercepts a network packet destined for the firstnetwork 104 of the client 102. In another embodiment, the client agent120 intercepts a network packet destined for a second network 104provided by a VPN connection to the appliance 200. In one embodiment,the client agent 120 intercepts a transport layer network packet at aninterface at the transport layer of the network stack 310, such as viathe transport driver interface (TDI). In other embodiments, the clientagent 120 intercepts a network packet at any layer at or below thetransport layer or layer 4 of the network stack 210, such as the networkor IP layer. In still another embodiment, the client agent 120intercepts a network packet at layer 4 and above, such as theapplication layer of the network stack 310.

The client agent 120, at step 615, identifies the application generatingor originating the intercepted request. In one embodiment, the clientagent 120 determines an identifier of the application via a system levelor kernel-mode function call. In one embodiment, the client agent 120determines via an application programming interface (API) the process id(PID) and/or the name of the application associated with the connectionor context from which the request was intercepted. In some embodiments,the client agent 120 determines an identifier of the application at thetime the client agent 120 intercepts the application's connectionrequest via the network stack 210. In other embodiments, the clientagent 120 determines an identifier of the application via inspection ofa payload of the intercepted request. In one embodiment, the clientagent 120 looks up or queries the application identifier from a datastructure, object, table, file or database. In another embodiment, theclient 120 associates or maintains an association of an identifier ofthe application with a transport layer connection of the application viathe agent 102 to the appliance 200.

At step 620, the client agent 120 transmits an identifier of theapplication, such as name or PID, to the appliance 200. In oneembodiment, the client agent 120 transmits the identifier of theapplication via the connection established at step 605, e.g., theapplication's transport layer connection to the appliance 200. In someembodiments, the client agent 120 transmits the identifier of theapplication to the appliance 200 via a header or field of the networkpacket. In yet one embodiment, the client agent 120 transmits theidentifier of the appliance 200 as part of the payload of a networkpacket transmitted to the appliance 200. In another embodiment, theclient agent 120 transmits the identifier of the application via acontrol or communication channel between the client agent 120 and theappliance 200. For example, the client agent 120 and appliance 200 maycommunicate information by a transport layer connection, such as TCP orUDP, established for exchanging information. In some embodiments, theclient agent 120 may make a remote procedure or function call to theappliance 200 to identify the application to the appliance 200. In oneembodiment, the appliance 200 associates the identifier of theapplication to the connection of the application established by theappliance 200. In yet another embodiment, the appliance 200 determinesthe identify of the application 200 upon a connection request of theapplication via the appliance 200 or by inspecting or analyzing contentof network traffic of the application via the appliance 200.

At step 625, the client agent 120 transmits an intercepted request ofthe application to the appliance 200. The request may be any type andform of network communication from the application. In one embodiment,the client agent 120 transmits a connect request of the application onthe client 102 to the appliance 200. For example, the application mayrequest to open a transport layer, SSL or TLS connection with theappliance 200 or to a server 106 via the appliance 200. In otherembodiments, the client agent 120 may intercept network communicationsof the application to be transmitted via the connection to the appliance200, and transmit the intercepted network communications to theappliance 200. In one embodiment, the client agent 120 transmits theidentification of the application with the transmission of theintercepted request. In other embodiments, the appliance 200 hasreceived from the client agent 120 identification of the application forthe connection to the appliance 200.

At step 630, the appliance 200 determines a level of access to providethe application of the client 102 based on the identification of theapplication and an associated policy. For the intercepted requesttransmitted at step 625, the appliance 200 determines from a policyassociated with the application, a level of access to provide to theapplication. In one embodiment, the appliance 200 received theintercepted request from the client agent 120, and looks up the policyfor the application associated with the request or the connection usedto transmit the request. In some embodiments, the policy for theapplication provided by the policy engine 236 identifies the type ofauthentication, access and/or auditing to apply to the interceptedrequest. In some other embodiments, the appliance 200 may determine whatto audit, the location of the audit log, and the type and level ofauditing to perform based on the identification of the application.

A policy may be associated with a list of one or more applications, byname of application, type of application or by pattern matching names ofapplications, such as all application beginning with “ms*.exe”, orending in a certain file type extension such as “*.pl. In someembodiments, the In one embodiment, the policy identifies for theapplication the type of authentication to perform. For example, thepolicy may indicate to request a certificate from the application totransmit to the intercepted request on the network 104′ or to the server106. In another example, the policy may indicate that the applicationmay need to perform two-factor or double authentication to be grantedaccess via the appliance 200. In some embodiments, the policy mayindicate the type of authentication based on the type of request of theapplication. For example, a first authentication type such as two-factorauthentication may be required for an open connection request to aserver 106, and a second authentication type for a query to a protecteddirectory on the server 106.

In another embodiment, the policy identifies a level of access via theappliance 200 to a network 104′ or server 106. In one embodiment, thepolicy identifies access is either granted or denied by the identifierof the application. For example, the appliance 200 may deny or grantaccess by an application with a specific name, such as “outlook.exe” or“msword.exe”. In another embodiment, the appliance 200 may grant accessto all applications unless the identifier of the application matches alist of one or more applications not to be given access via a policy. Insome embodiments, the appliance 200 may deny access to all applicationsunless the identifier of the application matches a list of one or moreapplications to be given access via a policy. In yet another embodiment,the appliance 200 may provide or assign one of a plurality of accesslevels to the intercepted request or application based on the identifierof the application. For example, a first application may be assigned aquarantined or limited level of access to a network 104 or server 106via the appliance. In another example, a second application may beassigned to a user group based on the name of the application, such asassigning the application named “perforce.exe” to an engineering usergroup, or the name of a financial or ERP application to a financial usergroup.

Based on the policy determination of step 630, the appliance, at step635, in one embodiment, the appliance 200 grants the application a levelof access via the appliance to one of a network 104 or server 106. Insome embodiments, based on the authentication provided by theapplication, such as receiving or not receiving a certificate, and theidentification of the application, the appliance 200 may assign thelevel of access of the appliance, such as downgrading or upgrade theaccess level. In one embodiment, the appliance 200 grants access by theapplication and transmits the intercepted request to its destination. Inanother embodiment, the appliance 200 grants access by the applicationon receipt of a first request, and then the appliance 200 allowscontinued access by the application after applying the policy to thefirst request. In some embodiments, the appliance 200 applies theapplication-based policy to each intercepted request transmitted via theappliance 200. In yet other embodiments, the appliance 200 appliesapplication-based policies to types of requests of the application.

In another embodiment, the appliance 200, at step 640, denies theapplication a level of access via the appliance to the network 104 orserver 106. In some embodiments, the appliance 200 based on theapplication-based policy denies any access by the application and dropsthe intercepted request. In other embodiments, the appliance 200downgrades the level of access by the application 220 and transmits theintercepted request according to the assigned level of access. In oneembodiment, the appliance 200 denies access by the application on a perrequest basis. On some requests of an application, the appliance 200denies access while on other requests the appliance 200 grants access.For example, the appliance may apply a per request policy based on thetype of request.

In some embodiments, the appliance 200, at steps 630, 635 and/or 640 maymake an authentication, authorization and/or auditing policy decisionbased on the identification of the application and any temporalinformation, such as the time of the request, the time the applicationestablished a connection via the appliance, and/or any temporal policyrules. For example, the appliance 200 may be authorized for accessduring a certain time period. If the appliance receives an interceptedrequest at time outside the authorized time period, the appliance 200may have a policy to deny access for the intercepted request.Additionally, the application based policies may be combined with useror group policies to make additional access, authorization andauthentication policy decisions to provide or not provide a level ofaccess by the appliance.

In view of the structure, functions and operations of the client agentand appliance described above, the client agent provides a finer grainof control over the network communications of the client to betransmitted via the appliance, such as via an SSL VPN connection. Theclient agent 120 may intercept communications by application name or anyportion and combination of the network or IP layer information, such asdestination and source IP addresses and destination and source ports. Inthis manner, the client agent 120 can be configured to interceptspecific network traffic patterns, such as traffic to a specificapplication, from a specific application, and/or between a specificsource end-point to a specific destination end-point. By interceptingand filtering network traffic at or closer to the client avoidsunnecessary network traffic being processed by the appliance and theappliance having to apply policies to protect the network. This providesadditional security to the network protected by the appliance as theclient agent does not transmit undesired network traffic to theappliance. Furthermore, the appliance provides finer grain control ofauthentication, authorization and auditing policies on a per applicationbasis, and even on a per request basis for each application.

1. A method for intercepting a communication of a client to adestination on a virtual private network based on a network destinationdescription of an application authorized to be accessed via the virtualprivate network, the method comprising the steps of: (a) intercepting,by an agent of the client, a network communication of the client, theagent establishing a virtual private network connection via an appliancefrom a first network to a second network; (b) determining, by the agent,a destination of the network communication corresponds to a networkidentifier and a port of a network destination description of anapplication on the second network authorized for access via the virtualprivate network; and (c) transmitting, by the agent in response to thedetermination, the network communication via the virtual private networkconnection.
 2. The method of claim 1, comprising determining, by theagent, the network communication does not correspond to the networkdestination description of the application, and transmitting the networkcommunication via the first network.
 3. The method of claim 1,comprising determining, by the agent, the network communication does notcorrespond to the network destination description of the application,and dropping the network communication.
 4. The method of claim 1,wherein the network destination description comprises one of an internetprotocol address and netmask, a single internet protocol address, or aninternet protocol address range associated with the application.
 5. Themethod of claim 1, wherein the network identifier comprises a host nameof a computing device hosting the application.
 6. The method of claim 1,comprising determining, by the agent, the network identifier and theport of the client corresponds to a source internet protocol address anda source port of the network destination description of the application.7. The method of claim 1, comprising determining, by the agent, a typeof protocol of the network communication corresponds to a protocolspecified by the network destination description of the application. 8.The method of claim 1, comprising determining, by the agent, not tointercept a second network communication of the client destined to asecond application not authorized for access to the second network viathe virtual private network connection.
 9. The method of claim 1,wherein step (a) comprises intercepting, by the agent, transparently toone of the application or a user of the client.
 10. The method of claim1, comprising receiving, by the agent, the network destinationdescription from the appliance.
 11. A system for intercepting acommunication of a client to a destination on a virtual private networkbased on a network destination description of an application authorizedto be accessed via the virtual private network, the system comprising: ameans for intercepting, by an agent of the client, a networkcommunication of the client, the agent establishing a virtual privatenetwork connection via an appliance from a first network to a secondnetwork; a means for determining, by the agent, a destination of thenetwork communication corresponds to a network identifier and a port ofa network destination description of an application on the secondnetwork authorized for access via the virtual private network; and ameans for transmitting, by the agent in response to the determination,the network communication via the virtual private network connection.12. The system of claim 11, comprising a means for determining, by theagent, the network communication does not correspond to the networkdestination description of the application, and transmitting the networkcommunication via the first network.
 13. The system of claim 11,comprising a means for determining, by the agent, the networkcommunication does not correspond to the network destination descriptionof the application, and dropping the network communication.
 14. Thesystem of claim 11, wherein the network destination descriptioncomprises one of an internet protocol address and netmask, a singleinternet protocol address, or an internet protocol address rangeassociated with the application.
 15. The system of claim 11, wherein thenetwork identifier comprises a host name of a computing device hostingthe application.
 16. The system of claim 11, comprising a means fordetermining, by the agent, the network identifier and the port of theclient corresponds to a source internet protocol address and a sourceport of the network destination description of the application.
 17. Thesystem of claim 11, comprising a means for determining, by the agent, atype of protocol of the network communication corresponds to a protocolspecified by the network destination description of the application. 18.The system of claim 11, comprising a means for determining, by theagent, not to intercept a second network communication of the clientdestined to a second application not authorized for access to the secondnetwork via the virtual private network connection.
 19. The system ofclaim 11, comprising a means for intercepting, by the agent,transparently to one of the application or a user of the client.
 20. Thesystem of claim 11, comprising a means for receiving, by the agent, thenetwork destination description from the appliance.